When mounting components on a printed circuit board using a component mounting machine there is a need for close precision. In order to achieve this an image processing device is often used for obtaining and analysing an image of the component after it has been picked up by means of a pick-up head. The aim of the analysis is to determine the exact position of the component on the pick-up head before it is mounted on the printed circuit board. When the position of the component to be mounted is known, the component mounting machine can compensate for the translation and rotation of the component before it is mounted on the printed circuit board. During the analysis, the image is compared with stored mechanical data of the component in order to be able to determine the position of the component to be mounted. For example, the positions of objects in the image corresponding to leads on the component to be mounted are compared with stored mechanical data that describe the nominal positions of leads on the relevant type of component. Furthermore, in the analysis the component to be mounted can be examined for faults, such as missing leads, erroneous leads or incorrectly positioned leads.
To be able to do the above analysis, component mounting machines are provided with a database with mechanical data for the most common components. However, due to the large amount of new components that are continuously introduced on the market the databases need to be continuously updated with mechanical data for these new components. Furthermore, for cases where the components to be mounted are components that are more rare, the database may not include mechanical data for this type of component. Hence, the database needs to be updated with mechanical data for these rare components when they are to be used.
Today, when updating the database with mechanical data for a component, the mechanical data are often derived from drawings or the like of the component and entered into the database manually. This is a time consuming task and there is always a risk that data is erroneously entered due to the human factor. Furthermore, in some cases drawings of the component are not available or the form of the available drawings are not suited for extracting the mechanical data of interest. Consequently, alternative methods that are automatic or semi-automatic have been developed where pictures of a single specimen or a number of specimens of a component are taken. The mechanical data for the single specimen or an average of the mechanical data for the number of specimens is then determined and stored in the database. The specimens used in this method are preferably specimens that have been produced with a very close precision.
The automatic methods have several disadvantages to the manual method. One disadvantage is that the mechanical data that are the result of any of these methods will differ to some extent from the mechanical data for a correct specimen of the component. This is due to the fact that the mechanical data stored are mechanical data for specimens of the component. These specimens may be rather exact but they always involve some errors in respect to the nominal mechanical data for the component. Another disadvantage is that it is difficult to calibrate the image processing device in order to get a correct scale in the image.